Puzzle 18: You have the misfortune to own an unreliable clock. This one loses exactly 20 minutes every hour. It is now showing 4:00am and you know that is was correct at midnight, when you set it. The clock stopped 4 hours ago, what is the correct time now?
Solution: 10 am
Explanation: 10:00am: Since the clock is losing 20 minutes every hour, for every real hour that has passed, the clock will only show 40 minutes. Since the clock shows 4:00am, we know that 240 clock minutes have passed. This therefore equals 360 real minutes and hence 6 hours. The clock stopped 4 hour ago and the time must now be 10:00am.